In integrated circuits, and CMOS circuits in particular, changes in state of a device such as an inverter can cause emission of light, such as infrared light. Whilst relatively low in power, such emissions can be detected, particularly if integrated over time while the circuit is in operation. Given sensitive enough equipment and enough time, it may be possible to determine sufficient information about the operating parameters of the integrated circuit to compromise information that it stores or processes.
It would be desirable to provide an integrated circuit with a mechanism for hindering optical detection of a pattern of light emitted by one or more active devices in an integrated circuit.